Cardiovascular disease has become a leading cause of global morbidity and mortality that annually results in 17 million deaths worldwide, many of which are caused by cardiac arrest. CPR is one of the most commonly used medical procedures for treating cardiac arrest. CPR may generate blood flow by directly increasing a patient's intrapleural pressure (chest compression mechanism) or by directly compressing the heart (heart pump mechanism) so that some life-sustaining blood flow can be maintained to the brain and other vital organs.
The 2010 American Heart Association Guidelines for CPR & ECC emphasized that a key to the successful resolution of a patient in cardiac arrest is to perform high-quality CPR as early as possible. High-quality CPR is defined as a compression frequency of at least about 100 times per minute and a compression depth of at least about 5 cm. Even with such high-quality CPR, however, cardiac output (CO) may reach about ¼ or ⅓ of normal CO. In clinical practice, manual or mechanical compression is often used. However, both methods are commonly associated with insufficient compression frequency and/or depth which can lead to poor CPR. Therefore, in the process of cardiac resuscitation, the CPR quality should be monitored. Although the CPR Guidelines recommend end-tidal carbon dioxide (ETCO2) and invasive blood pressure monitoring for determining CPR quality, these methods require either additional specialized medical devices (ETCO2) or time-consuming procedures (invasive monitoring) which make them less practical for routine clinical practice.
High-quality CPR should also involve little compression interruption. In 2013, the AHA recommended that compression time should amount to at least about 80% of an emergency treatment process. During this process, however, compression interruption may often occur due to endotracheal intubation, rescuer changeover and/or electric defibrillation. Moreover, too much compression interruption will bring about reduction in both coronary perfusion pressure and restoration rate of spontaneous circulation (and even in forward neurofunction prognosis after restoring the spontaneous circulation). Until now, there has been no monitoring means convenient for reminding the rescuer of the compression interruption situation. Although blood oxygen monitoring can show pulse oximetry waveforms caused by compression for a patient exhibiting cardiac arrest, judgment is still required as to whether there is compression interruption by manually observing the pulse oximetry waveforms, and it is impossible to measure the compression interruption time early enough for a warning.